JBL 75.4 Amp + Where to put Nokia Car Kit / mute lead??

[Jon]

Hi all,
Ive just got my new amp (JBL 75.4) after the old freebie one went pop.

The system at the moment is a bog standard sony head unit with the
speaker wires going via a mute lead for my phone kit straight to the
speakers - all works well (but stereo is quiet).

When I re-wire to accomodate the new amp I will use the low level
outputs from the head unit and connect to the low level inputs on the
amp. Speaker wires running to the speakers from the amp.

The question is where to I put the mute lead / box for the car kit?
Can I simply take the wires that go from the amp to the speakers and
put the mute lead in the middle or will this damage the mute relay?

Previously when I had the amp connected (not using low level
connectors), even when the Nokia phone was set to minimal volume, the
amp was upping the volume too much such that half the town could here
the conversation!

Is there another way, utilising the equipment I have? I dont want to
use the CD changer port as a line in as this is reserved for my ipod
connector.

Also, if I only use 2 speakers (its going in a Landrover so no
brilliant sound system!) what is the best way to utilise the amp -
should I bridge or just use 2 channels, leaving the other 2 empty?

Speakers are Sony 6x9s


Thanks
Jon

[In-Car Express]

Post by Jon
The question is where to I put the mute lead / box for the car kit?
Can I simply take the wires that go from the amp to the speakers and
put the mute lead in the middle or will this damage the mute relay?

If you're using low level input, it'll need to go between the amp and
speakers. You'd need to check that the mute lead either isolates the
amp outputs by relay, or that it's of sufficiently high power
capacity. If it's not, you could achieve the same thing yourself with
a couple of relays.

Post by Jon
Also, if I only use 2 speakers (its going in a Landrover so no
brilliant sound system!) what is the best way to utilise the amp -
should I bridge or just use 2 channels, leaving the other 2 empty?

Bridging it will give it more power, effectively increasing it's
damping factor at lower volumes, so I'd do it that way - just make
sure the gain controls are set in a way which prevents excess power
going to the speakers.

Jon

[Jon]

Post by In-Car Express

Post by Jon
The question is where to I put the mute lead / box for the car kit?
Can I simply take the wires that go from the amp to the speakers and
put the mute lead in the middle or will this damage the mute relay?

If you're using low level input, it'll need to go between the amp and
speakers. You'd need to check that the mute lead either isolates the
amp outputs by relay, or that it's of sufficiently high power
capacity. If it's not, you could achieve the same thing yourself with
a couple of relays.

The mute lead works by relay - when it cuts in/out you can definately
hear it clicking. So based on your reply I guess it should be OK.

Post by In-Car Express

Post by Jon
Also, if I only use 2 speakers (its going in a Landrover so no
brilliant sound system!) what is the best way to utilise the amp -
should I bridge or just use 2 channels, leaving the other 2 empty?

Bridging it will give it more power, effectively increasing it's
damping factor at lower volumes, so I'd do it that way - just make
sure the gain controls are set in a way which prevents excess power
going to the speakers.

Sorry to be thick, but what is "damping factor"?

Thanks
Jon

[In-Car Express]

Post by Jon
Sorry to be thick, but what is "damping factor"?

I had a feeling that might be the next question! It's probably one of
the hardest to explain concepts going, but is basically a measure of
the amp's ability to react to changes in the load it's driving.

As a speaker moves in and out, it's impedance changes. As the
impedance of the speaker changes, the current required to move it
increases and decreases. Damping factor is a measure of the amp's
ability to deal with the changing current demands that the impedance
change causes, without changing the output voltage.

If you run an amplifier so that it never has to fully utilise it's
full internal voltage capacity, it's damping factor is inherently
increased, giving a better controlled, and hence more accurate
sounding output.

Jon

[Jon]

Cool. Sounds like bridging is the way forward.

Many thanks for your reply.

I'll see how I get on over the weekend.

Jon

On Fri, 4 Nov 2005 13:26:00 +0000 (UTC), In-Car Express

Post by In-Car Express

Post by Jon
Sorry to be thick, but what is "damping factor"?

I had a feeling that might be the next question! It's probably one of
the hardest to explain concepts going, but is basically a measure of
the amp's ability to react to changes in the load it's driving.
As a speaker moves in and out, it's impedance changes. As the
impedance of the speaker changes, the current required to move it
increases and decreases. Damping factor is a measure of the amp's
ability to deal with the changing current demands that the impedance
change causes, without changing the output voltage.
If you run an amplifier so that it never has to fully utilise it's
full internal voltage capacity, it's damping factor is inherently
increased, giving a better controlled, and hence more accurate
sounding output.
Jon

[Jon]

Well I finally got everything sorted last night.

Low level inputs to amp (Rear L & R only).
Bridged pair of speakers
Phone Mute lead afetr amp in speaker wires

All works great, but just a few questions...

1. Should I be able to hear a faint hissing noise from the speakers
when all is powered up but volume on head unit turned right down??
With the engine on (2.5L Diesel) its not audiable. If not, any
suggestions as to what may be the cause?

2. Can I use the low level "Front" input that are currently not used
for another source - iPAQ / TomTom? I know that the stereo wont cut
out when she starts talking to me but thats not a problem.


Thanks guys...
Jon

Post by In-Car Express

Post by Jon
The question is where to I put the mute lead / box for the car kit?
Can I simply take the wires that go from the amp to the speakers and
put the mute lead in the middle or will this damage the mute relay?

If you're using low level input, it'll need to go between the amp and
speakers. You'd need to check that the mute lead either isolates the
amp outputs by relay, or that it's of sufficiently high power
capacity. If it's not, you could achieve the same thing yourself with
a couple of relays.

Post by Jon
Also, if I only use 2 speakers (its going in a Landrover so no
brilliant sound system!) what is the best way to utilise the amp -
should I bridge or just use 2 channels, leaving the other 2 empty?

Bridging it will give it more power, effectively increasing it's
damping factor at lower volumes, so I'd do it that way - just make
sure the gain controls are set in a way which prevents excess power
going to the speakers.
Jon